(With 9 Charts.) IN our previous studies on the spread of bacterial infection among mice, the resistance of the host has not been especiallv investigated; although the importance of this factor has been repeatedly referred to in discussing the experimental results obtained.The recent reports on experimental epidemiology from the Rockefeller Institute contain many references to this aspect of the question, and, in particular, the careful and important investigation reported by Webster (1922) affords ample evidence of the possibility of conferring some degree of immunity on mice by the administration of dead or living suspensions of bacteria of the B. enteritidis group, whether by feeding or by inoculation.The experiments recorded in the present report were undertaken in order to study any differences, which might occur in the mode of spread of enteric infection among mice, when the immunity of the population at risk was varied by including, among the normal and presumablv susceptible mice, a varying proportion of artificially immunised animals.Consideration of the results obtained during the past five years, both in experiments which have formed the subject of reports and in many others not yet recorded, has led us to believe that the question of immunity as an attribute of a herd should be studied as a separate problem, closely related to, but in many ways distinct from, the problem of the immunity of an individual host. Experiment 1. For the purpose of this, and of the next experiment, a vaccine was prepared from a strain of B. enteritidis (Aertrycke). This was killed by heat, standardised to contain 4000 million bacteria per c.c., and preserved by the addition of 05 per cent. phenol.In the present experiment 127 mice were given an intraperitoneal injection of 0125 c.c. (500 million bacteria). Eight days later there were 119 survivors, and each of these was inoculated intraperitoneally with 0-25 c.c. of vaccine (1000 million bacteria).The main experiment was started 21 days after the second injection. Four of the immunised mice were killed on this day, and their sera were tested

We are sorry to commence a review of the second edition of a book that is m our opinion by far the

No abstract

IN several previous reports we have described the behaviour of communities of mice, submitted over long periods of time to the risks attendant on the epidemic prevalence of a bacterial infection. These communities have been recruited in ways varying both as regards the rate of immigration and the nature of the immigrants.The present report deals with an experiment in which we have studied the effect of prophylactic immunisation, with a suitable bacterial vaccine, in modifying the course of events in our experimental herds.As in many of our previous experiments, the infection selected for study was mouse typhoid, due to infection with Bact. aertrycke. There is abundant evidence that the active immunisation of mice with killed suspensions of this organism results in an increased resistance to subsequent experimental infection with living cultures (

(With 2 Charts.) 1N a previous communication (1921) experiments have been described showing the effect produced by continuously adding normal nice to a cage, the population of which is infected with bacilli of the group which includes B. gaertner and B. suipestifer. It was seen that under these circumstances the spread of infection progresses in a series of epidemic waves, and that the survival-time of any batch of nlice varies according to tb e period at which they are introduced to the cage. It was further shown that, if such regular and continuous addition of susceptible animals be persisted in over long periods of time, all the mice will eventually succumb, while, if the addition of new individuals be discontinued, the epidemic will eventually subside, leaving a proportion of survivors who may remain in apparently good health over a considerable period.In one experiment, in which an infected population was thus kept isolated for 77 days after the last addition had been made to the cage, the 15 survivors were killed and examined post-mnortem. From nine of them the orgainisnms which caused the epidemic were recovered. It therefore seemed probable that a condition of equilibrium had been attained between the parasites and their hosts, which might be maintained indefinitely so long as the surviving population was kept isolated from susceptible individuals of the same species. The experimnents outlined in the present report were undertaken in order to ascertain how this equilibrium would be affected by the addition to the cage of a relatively large number of normal animals.Two experiments have so far been carried out on mice infected with B. gaertner and B. stuipestifer. It has already been noted that infection with either of these organisms produces a disease whicb is indistinguishable from that produced by the other, and that if an epidemic be started by feeding mice on a culture of B. gaertner, B. suipestifer may be isolated from a high proportion of the animals subsequently dying, either alone or associated with the former organism.